Volume 2006, Issue 207,
July 2006

Extracted from text ... Southern African Forestry Journal - No. 207, July 2006 1
Editorial Comment
"Seventy tree stories from Africa"
The above is the title of an encouraging booklet by Jean-Yves Clavreul
With running title "Trees : An effective means of combating desertification"
Copyright Les Editions Gannadal 2003
Editors CTA, Postbus 380, Wageningen, Netherlands
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The Technical Centre for Agricultural and Rural Co-operation (CTA) was established in 1983 under the Lom?
Convention between ACP (African, Caribbean, Pacific) Group of States and the European Union Member
States. Since 2000, it has operated within the framework of the ACP-EC Cotonou Agreement
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In the Preface ..

Early studies suggest that the juvenile period, during which favourable rooting can be achieved from <i>Pinus patula&lt;/i&gt; seedling hedges, may be as short as 2 years from the date of sowing. If the effects of hedge maturation cannot be delayed, productivity from seedling hedges will be severely limited. The most common technique
to postpone hedge maturation in some coniferous species is by rejuvenating the donor plant (ramet) through
serial propagation or hedge cycling. This involves taking a cutting from the parent hedge and, once rooted,
establishing a new donor hedge from the rooted cutting. Cuttings harvested from such cycled hedges have been
reported to grow better than those from non-cycled hedges that have passed the point of ontogenetic
maturation. This paper summarises the effects of cycling <i>P. patula&lt;/i&gt; hedge plants in the nursery on subsequent
field performance. Seedling comparisons were included in the field trial. The effects of cycling were measured
for the first three years after planting. The field results indicate that cycling hedges within the first 24 months
since sowing negatively affected early field growth in one treatment. Cuttings from the non-cycled three-yearold
seedling hedge treatment performed similarly to the seedling controls in the field trial, which supports
other studies. Based on these results, it is currently recommended that <i>P. patula&lt;/i&gt; cuttings be produced from
seedling hedges for a period of 36 months from sowing, without the inclusion of a hedge-cycling regime.

Propagation of African sandalwood <i>(Osyris lanceolata)&lt;/i&gt; by air layering (marcotting) was investigated at
Sao Hill, Tanzania, aiming at providing an alternative propagation technique to the use of seeds or
cuttings that germinate or root poorly. Air layers were initiated on the young shoots (1 - 2 years old) of
mature <i>O. lanceolata&lt;/i&gt; trees growing at Sao Hill catchment Forest. After root initiation, which took 8
weeks, they were detached from the parents, potted in polyethylene tubes and reared at the nursery for
a further three months. The factors assessed in this experiment were the effect of time at which air layers
were initiated (i.e. February, June, September and December); and the influence of IBA as rooting
promoter at three concentrations (50, 100 and 150 ppm). From the data collected it was observed that
rooting success of up to 80% can be achieved from air layers, making this propagation technique a viable
alternative to seedlings or cutting propagation. Rooting success was influenced by both the season and
application of rooting hormone with optimal rooting being achieved during June and September with the
addition of IBA at a rate of 50 ppm. The significance increase in rootability of air layers during June and
September may be linked to the advantage of the dry season in Tanzania where reduction of plant
development activities such as budding, leafing and flowering in the dormant dry season might have
reduced resource competition and thus promoting the observed rooting.

Many cold tolerant eucalypts, <i>E. macarthurii&lt;/i&gt; in particular, coppice vigorously following harvesting, and
in contrast to <i>E. grandis&lt;/i&gt; are proving difficult to kill by existing cut stump control methods. Based on past
research, selected cut stump treatments were tested on single stem <i>E. macarthurii&lt;/i&gt; trees, that had not
been coppiced, in Paulpieterburg, KwaZulu-Natal. These included the application of the herbicide
triclopyr (amine salt, 360 g l<sup>-1</sup>), alone, or in combination with glyphosate (isopropylamine salt, 360 g l<sup>-1</sup>),
either to the cut-surface, or to a basal frill. Due to the uncertainty as to the efficacy of these treatments
for killing stumps of species other than <i>E. grandis, &lt;/i&gt; the above treatments were integrated with current
harvest residue management operations (burning; the piling of harvest residues on top of stumps; removal
of the harvest residues away from the stumps) to determine if any of these further reduced the level of
coppicing. Compared to the removal of slash away from the stumps, the burning, or piling of slash on top
of the stumps resulted in a significant but small reduction in coppice regrowth. At the rates tested both
herbicides killed 83-90 % of the stumps, irrespective of how they were applied (basal frill or cut surface).
This result has important commercial implications as it will allow the forest companies the flexibility to
choose the herbicides, and (or) manner in which they are to be applied.

Black wattle <i>(Acacia mearnsii de Wild)&lt;/i&gt; is a commercially important forestry species in South Africa,
however, being an exotic it is also seen as an invader of indigenous vegetation. Research into producing
a sterile variety is underway and one such route being explored is the production of a polyploidy. Within
this research it is critical to have reliable and affordable methods to identify the polyploids from the
normal diploid material, one such method identified is using chlorophyll content. A practical limitation
of this method is that many of the samples being tested are in the field and away from the laboratory and
thus research has been aimed at storage of the samples as a means to preserve the chlorophyll prior to
absorption spectral analyses.
<br>The effects of storage of leaves on chlorophyll content were determined in five non-identical two yearold
nursery diploid black wattle genotypes. Fifteen leaf samples from each genotype were either oven dried
and then stored for one week or one month at room temperature, or frozen for one week or one month at
-4 <sup>o</sup>C, before chlorophyll was extracted and absorbance spectra determined. Chlorophyll absorbance values
were assessed at three peaks, namely, 433 nm, 456 nm and 663 nm. Chlorophyll extracted from leaf
material on the day of collection (day-0) was used as the control. Assessment of the total mean chlorophyll
absorbance (TA), sum of the three peak absorbance mean values (Â), revealed significant differences
between all treatments (p < 0.01) as well as significant differences (p < 0.01) from the control (TÂ = 1.275).
Chlorophyll absorbance values within dried and frozen treatments were compared with respect to storage
time periods of seven days and 28 days. Dried leaves that were stored for seven days (TÂ = 1.132) resulted
in the least amount of chlorophyll degradation followed by 28 days ice storage (TÂ = 1.114), seven day ice
storage (TÂ = 1.103) and lastly 28 days dried storage (TÂ = 1.093). Analysis of variance revealed that
within individual plants, the chlorophyll absorbance values between wavelengths, were significantly
different (p&lt; 0.05). It was noted that whilst all treatments decreased from the control (day-0), dried
samples decreased steadily over time whereas a similar trend for frozen samples could not be identified.

In 1995 a forest inventory covering northern Namibia was initiated, based on stratified systematic field sampling of plots with a radius of up to 30 m. In these plots detailed tree parameters were measured. Due to security problems the most important wooded parts of the area could not be covered. This study
investigated whether Landsat TM imagery could be used to estimate woody vegetation parameters. As
the existing field sampling method did not result in significant relationships between pixel values of
different bands and tree cover, two sampling methods of different design were tested. Both resulted in
statistically significant relationships between tree cover and pixel values of mainly band 4 reflectance of
Landsat TM. Regression equations to estimate cover and volumes were obtained. The increased size of
the sample plots in both methods was the main reason for improved correlations. The relation between
tree cover and Landsat TM band 4 was influenced by fire scars and patches of heavy grazing. Estimated
tree cover and volumes obtained by remote sensing were compared with volume estimates obtained by field
inventories. All fell within 95 % confidence limits of the field estimates. The results suggest that Landsat
TM imagery is suitable for estimating tree cover, volumes and biomass on a regional scale for dry semideciduous
Kalahari woodland vegetation. More research is needed to better understand the impacts of fire
and heavy grazing on cover estimates and future inventories should use larger sample plots.

Soils were sampled around live fences of <i>A. laeta&lt;/i&gt; and <i>A. mellifera&lt;/i&gt; plots in an experimental research site of
the Senegalese Institute of Agricultural Research at Bambey, Sénégal. They were collected before and after
the rainy season at three distances (1 m, 3 m and 5 m) and two depths (0-25 cm and 25-50 cm). Roots were
extracted using the wet sieving method and their concentrations were evaluated. Arbuscular mycorrhizal
colonization (% of total roots length) was assessed after staining and observation under a compound
microscope. Spores were extracted from soils by sucrose centrifugation and counted under the microscope.
Root concentrations (cm per 100 g of dry soil) were greater on <i>A. mellifera&lt;/i&gt; than on <i>A. laeta&lt;/i&gt; for all seasons,
distances and depths. For each species studied, root concentrations were greater at 1m from the live fence
and at 0-25 cm of depth. The intensity of mycorrhizal colonization was greater on <i>A. mellifera&lt;/i&gt; (66%) than
on A. laeta (42%). For both tree species level of colonization was higher after the rainy season but A. laeta
root colonization seems to be more affected by rain than in the case of <i>A. mellifera</i>. Mycorrhizal colonisation
was not affected by distance from the live fence or by soil depth. Spore number (in 100 g of dry soil) was
generally low (37.5 spores) and did not vary between seasons and between distances. Spores were more
numerous under <i>A. mellifera&lt;/i&gt; fence (42.43 per 100 g dry soil) than under <i>A. laeta&lt;/i&gt; fence (33.28 per 100 g dry
soil). Its number decreased from 0-25 cm to 25-50 cm depth. Generally, positive coefficient correlations were
higher between root concentration and root infection than between root concentration and spore number.
Low correlation was also found between infection and spore number. Given its numerous qualities,
<i>A. mellifera&lt;/i&gt; appears to be more promising in live fences than <i>A. laeta</i>.

Pot-binding can adversely affect the performance of container-grown stock. One factor that affects potbinding
is the size of the root system in relation to the size of the container. The aim of this study was to
determine if an objective root-bound index (RBI) would be useful when evaluating the quality of pines grown
in various types of containers. A RBIdia was determined by dividing the root-collar diameter (RCD) by the
cavity diameter (i.e. the distance from one container wall to the opposite container wall, measured at the
top of the container cavity and passing over the centre of the cavity) and a RBIvol was determined by dividing
the RCD (mm) by the container volume (ml). Field assessments of seedlings produced in six container types
in the United States indicate that both RBI methods produced similar results for survival of <i>Pinus palustris</i>
(stock with the highest RBI values exhibited the lowest survival). However, the RBIvol method did a better
job of separating the performance of two types of peat pots. Both indices were also related to outplanting
performance of P.&lt;i&gt; patula&lt;/i&gt; cuttings grown in South Africa. When sorting container stock, <i>P. elliottii x
caribaea&lt;/i&gt; cuttings with RBIvol values greater than 7 might be culled while <i>P. palustris&lt;/i&gt; seedlings might be
culled when the RBIvol index exceeds 11. Therefore, the target RBIvol value will vary with species and plant
type. When tree planting guides cover a range of container types, listing a maximum RBIvol value would
provide some indication of when root-binding might reduce plant quality. In addition to RBI, the age of the
roots also appears to affect field performance of pot-bound stock. We rejected the hypothesis that age is not
related to post-planting survival of <i>Pinus elliottii x caribaea&lt;/i&gt; cuttings.

The context of the study is the concern over declining provincial road conditions due to insufficient
government funding for road maintenance. The roads are used by a wide variety of commercial and private
interests that contribute a broad range of axle loads. There is no information available on the use of these
roads, nor on their condition from forest companies and other users. A nation-wide survey, in the form
of a questionnaire, was subsequently conducted to determine the condition and length of each segment
of provincial road in use by forest companies, as well as the volume of wood transported over them. In
addition, an attempt was made to gather data on other road users over each section of road surveyed.
<br>The questionnaire results show that there is great degree of variation in the condition of provincial
roads, with 50% of them being serviceable over only 50% of their total lengths. There is a 20% reduction
in the road condition during wet periods, which would indicate poor drainage and/or use of poor quality
road building materials. The literature reviewed suggested that maintaining or rebuilding these roads
could result in a significant reduction in total transport costs. Round wood transport contributes the
majority of the axle loading to these roads, and forest companies therefore need to take responsibility for
damage caused to them, as well as their maintenance. Of the total length of provincial roads surveyed,
38% is used by two or more forest companies, representing 47% of the total volume hauled. As a result,
road maintenance collaboration between companies is needed.

Mechanical, manual, thermal, biological and chemical methods of managing forest vegetation have, to
a large extent, been developed independently. The effectiveness and relatively low cost of chemical
herbicides, however, have led to systems of vegetation management that rely on their continued
availability and the near exclusion of non-herbicide methods for controlling forest weeds. Greater public
concern, perceptions of risk, and pressures exerted by some forest certification systems, have increased
the need to provide a wider array of alternative methods that can reduce dependence on herbicides. In
response, forest vegetation management research has widened to include investigations of alternatives
to herbicides, along with initiatives aimed at reducing chemical use. An international review of progress
indicates that reduced herbicide use may already be possible in many countries. There are however, a
number of commercial, economic and social issues associated with the practical application of this
knowledge, notwithstanding the fact that a more integrated approach is required to combine relevant
methods of vegetation management, rather than attempting to practices alternative techniques in
isolation from other silvicultural practices. This paper, together with appropriate examples, reviews
pressures to reduce herbicide use as well as past and current research to develop alternatives to herbicides
in eleven different countries, as well as identifying instances of the successful or unsuccessful
implementation of this technology.